John Duffy and David Mulcahy

His early career focused on how environments like buildings or cities shape behaviour, and moved on to explore how we act in emergency situations.

But in 1985, when police asked for his help on what became known as the Railway Rapist case, David applied his rigorous methodology to help track down the offender – and changed the course of criminal profiling in the process.

Since then, he's contributed to numerous investigations and given evidence in court cases, authored influential books, and built an entire discipline from the ground up.

And he's also found time to get a PhD in music composition as well.

And then they had a series of rapes and murders around London.

And they asked me if I could, the way they put it, could you help us catch this man before he kills again?

So this is what the media dubbed the railway rapist.

And you were applying your new methodology to this case, what would become investigative psychology.